Acid mine drainage issue reaching critical stage – WRC

JOHANNESBURG (miningweekly.com) – The issue of mine water treatment and the management thereof has become urgent. South Africa has run out of time to debate and must act, says Water Research Commission (WRC) mine water treatment and management research manager Dr Jo Burgess.
The western, central and eastern basins of the Witwatersrand are currently the main focus of South Africa’s acid mine drainage (AMD) treatment needs, Department of Water Affairs (DWA) water-quality management senior manager Marius Keet tells Mining Weekly.
“The issue of AMD was elevated to a political level about two years ago and Cabinet approved recommendations to deal with AMD in the Witwatersrand in February last year, after which the Trans-Caledon Tunnel Authority (TCTA) was appointed to deal with the situation,” says Keet.
The TCTA has already implemented what the DWA calls the immediate solution.
“In the western basin, we have managed to stop the decant and draw the water down to one metre below surface level. However, this was before the rains started, which will cause the water to rise again,” he states.
If the DWA had enough pumps and treatment facilities, it would be able to draw the water down to the environmental critical level, which is 150 m below surface and which would create a buffer capacity if it rained, he adds.
In terms of the central basin, the DWA is still waiting for final budget approval for the construction of the treatment plant for the next financial year, says Keet, adding that the necessary funds for this year have been made available.
“I am positive, except for the fact that we will run out of time if something is not done within the next few weeks,” he says.
Building a treatment plant takes about a year and the current situation dictates that the environmental critical level will be breached in June or July next year. Therefore, there is only nine months left during which to act, he explains.
Further, as a result of financial constraints, the DWA has decided to defer the treatment of the AMD from the eastern basin to a later stage, as the eastern basin’s situation is less critical than that of the central and western basins.
“The eastern basin is also critical, but we do have some time,” says Keet.
The DWA is also looking at alternatives in the western basin to build a fully conventional, high-density sludge treatment plant in an attempt to cut costs.
“We are investigating the possibility of upgrading the current Rand Uranium treatment plant to a level where it will have the capacity to draw the water level in the basin down to more than one metre, where it is currently.”
Sustainability
The current treatment method used by the DWA, known as neutralisation, is not sustainable over the long term.
“Neutralisation removes the heavy metals from the water but not the sulphates. As long as sulphates are released into the country’s water resources, the country is relying on there still being enough water to dilute the sulphates without polluting the water to an unusable level,” global strategy consultancy AT Kearney principal Martin Sprott points out.
“As more basins start to decant, the Vaal system will not be able to dilute the water. We have until 2015, when the river system will no longer be able to dilute the water sufficiently, which makes neutralisation unsustainable,” he adds.
The DWA is undertaking a feasibility study to find long-term solutions for AMD in the Witwatersrand, which should be completed in February next year.
Meanwhile, the University of Cape Town’s Professor Alison Lewis is researching crystallisation as a method to treat contaminated water such as concentrated AMD.
Eutectic freeze crystallisation (EFC) reduces the temperature of the water stream to the eutectic point at which ice and a pure salt will crystallise. Ice, which has a lower density than water, will float, while salt, which has a higher density, will sink, Lewis explains.
The benefits of EFC include no added chemicals, pure water and pure usable salts can be recovered and freezing is much less energy intensive than evaporation, she adds.
To date, EFC has not been used to treat AMD.
However, EFC can improve South Africa’s current AMD crisis, as it is potentially a zero-waste process, which not only makes it sustainable but also ideal for use on a large scale, says Lewis.
Challenges
The difficulties pertaining to the treatment of AMD are mostly not scientific or technical, but rather involve institutional arrangements and funding, WRC groundwater research manager Dr Shafick Adams tells Mining Weekly.
“More than 20 different models for treating all the types of mine water have been developed worldwide, so the issue is not that people do not know how to treat the water,” he adds.
Most of the challenges stem from identifying who should be responsible for paying for the treatment, the type of water that is produced through the treatment and where the treated water and by-products should be sent, Burgess explains.
In other parts of the country, such as Mpumalanga, there are mining houses that, in collaboration with local communities and municipalities, are protecting the immediate resources around the mines and dealing with local AMD threats, Sprott points out.
However, the Gauteng area is a specific challenge, as there are no active mining companies taking responsibility for the AMD.
“This is understandable, as these companies are currently not mining there and, in many cases, have never mined there before. Therefore, they cannot be expected to take over a legacy problem and this is why the treatment of AMD needs to be taken to a national level,” Sprott adds.
Keet agrees that AMD is a legacy problem in terms of companies who have mined and left, environmental laws that were not strict enough and a lack of interaction among government departments.
“In the past, interaction among the DWA, the Department of Mineral Resources (DMR) and the Department of Environmental Affairs was not as good as it should have been. However, Water and Environmental Affairs Minister Edna Molewa and Mineral Resources Minister Susan Shabangu have since intervened and have established a committee at ministerial level to discuss these issues,” Keet says.
Problem or Opportunity
“AMD isn’t unique to South Africa, but the difference is that here it is seen as a problem, while in other parts of the world it is often seen as an opportunity,” Sprott says.
Gauteng is forecast to reach a balance between the supply and demand of water in 2015, as there is not enough water coming from the Lesotho highlands to cover the needs of the population. Simultaneously, there is a huge amount of water lying under the rand area, which could, if treated to potable level, delay the time during which the province will run short of water. This will allow more time to find a sustainable long-term solution, Sprott explains.
Meanwhile, Mining Weekly reported in July that Professor Frank Winde of the North West University stated at this year’s Sustainability Week that untreated AMD could possibly be used by municipal sewerage works to aid nitrate digestion, thus eliminating water- treatment costs, while also saving clean water, which would otherwise have been used for this.
The BioSURE treatment process is built on this principle and is being considered by the DWA as part of the long-term solution, Keet says.
“However, while it is an ideal situation, it is not necessarily practical, as the process requires vast amounts of sewage, which cannot always be found close to mining houses,” he adds.
Burgess points out that the cotreatment of mine water with other waste often results in better treatment of the mine water and the waste, adding that it is important to take into account that the water disposed of by every mine is different.
“For cotreatment you need the right combinations of the quantity and quality of the AMD as well as the quantity and quality of the waste; therefore, cotreatment can be perfect for some situations, while being unsuitable for others,” she adds.